Due to health and environmental concerns over the use of synthetic pesticides, there is a growing trend toward the use of natural or biorational pesticides which have little or no harmful environmental effects. As disclosed, e.g., in U.S. Pat. No. 4,556,562, one such natural pesticide is azadirachtin which is derived from the seeds of the neem tree (Azadirachta indica A. Juss). The neem tree is indigenous to a number of middle and far east countries, e.g., India, Pakistan, Bangladesh, Myanma, Thailand, Malaysia, and parts of Africa.
As described in the aforementioned patent, azadirachtin is typically extracted from the neem seeds along with neem oil which is a triglyceride component also found in neem seeds. The neem oil is reported to protect azadirachtin from ultra-violet degradation.
Neem oil containing the azadirachtin is typically applied to crop seeds or sprayed on the growing crops as an emulsion. Such crop seed or crop treatment deters insects from feeding on the crop, exhibits a growth regulating effect on the insects and interrupts insect propagation. Some insects against which azadirachtin has been found effective include Japanese beetles, fall armyworms, locusts, termites, grasshoppers, tobacco hornworms, tobacco budworms, caterpillars, gypsy moths, rice weevils, aphids, cotton boll moths and the like. Also, azadirachtin-containing neem oil emulsions may be incorporated into insect repellent products, e.g., soaps, sprays, lotions or the like for human or animal use.
However, it is very difficult to form storage stable neem oil emulsions especially when using environmentally safe and acceptable emulsifying agents, i.e., those approved for use as food additives for human consumption under 21 CFR 172 as well as those approved for agricultural use under 40 CFR 180.1001(c),(e).